Getter for electron tube



Aug. 18, UTTLE GETTER FOR ELECTRON TUBE Filed June 20, 1957 l ,INVENTORJI HOWARD D.'DOOLIT TLE GENT United States 'GETTER FOR ELECTRON TUBE Howard D. Doolittle, Stamford, Conn., assignor to Machlett Laboratories, Incorporated, Springdale, Conn., a

corporation of Connecticut Application June 20, 1957, Serial No. 666,940

3 Claims. or. 313-178) V This invention relates to improvements in electron discharge devices and has particular reference to novel gettering means for electron tubes.

' In my copending application Serial Number 548,172, filed jointly with E. I. Naill and B. H. Wadia on November 21, 1955, there is described a novel cathode structure,

for coaxial high frequency type electron tubes, which :such' an electron tube and is primarily concerned with the provision of a strip or hollow cylinder of gettering material in a location within the tube Where it is most advantageously heated so that it may readily perform its function.

', a More particularly, I have found that a strip of gettering material may be secured directly upon a portion of the emitter by'means of an intermediate joint or connector formed of a material which will not readily alloy with eitherthe material of the emitter or of the getter at tube operating temperatures.

' As pointed out in the aforementioned copending application, the use of zirconium, tantalum, hafnium, titanium or the like in an electron tube as a gettering material is highly desirable, but has not been entirely successful because of the ditficulties encountered in positioning the material in close proximity to the parts of the tube which operate at the elevated temperatures necessary for the material to function properly as a getter. Such parts are normally made of a material, such as nickel, which alloys readily with the getter material.

'Acco'rdingly,'a primary object of the present invention is to provide an electron tube with an eificiently functioning getter of zirconium, titanium, tantalum or the like.

Another object is to provide a getter actually supported by and in close proximity to a heated part of the structure which is formed of a material known to readily alloy with the material of the getter.

Other objects and advantages of this invention will become apparent from the following description taken in connection with the accompanying drawing, wherein the figure is a front elevational view partly in axial section of an electron tube embodying a preferred form of the invention.

Referring more particularly to the drawing, the tube embodying the invention comprises a gas-tight envelope generally designated by numeral and havinga cylindrical metal terminal portion 11 at one end connected by a vacuum seal to one end of a glass or similar dielectric bulb portion 12. Within the envelope and supported by portion 11 is an axially disposed anode 13, portion 11 being the external terminal thereof. Concentric with anode 13 is a tubular grid terminal 14 which is sealed throughout one end to the other end of the dielectric bulb atent O 2 portion 12 of the envelope. A tubular grid support 15 is sealed at one end to the inner wall of grid terminal 14 and'carries on its other end a grid 16. The grid 16 is maintained in position on a flange formed on the inner end'of the support 15 by a retainer 17, and is disposed in predetermined spaced relation to the anode 13 and to a cathode structure 18 located coaxially therewith within the grid support 15.

The cathode structure 18 includes a first terminal formed by a pair of coaxial tubular members, an inner member 19 and an outer member 20, which are joined together adjacent the end of the tube and form a portion of the envelope 10. Outer member 20 is flared outwardly at 21 and is sealed by an annular dielectric insulating ring 22 to one end of an annular metal ring 23 which is in turn sealed throughout its opposite end to the inner surface of the grid support 15.

The inner tubular member 19 encircles and is sealed to the outer surface of a substantially tubular cathode supporting ring 24. The supporting ring 24 is in turn sealed by an annular insulating member 25 to the inner end of a second tubular terminal 26 which extends coaxially within and in spaced relation to the first cathode terminal 1920.

The inner end of the cathode supporting ring 24 has secured to it one end of a cathode support member 27 which consists of a tubular foil formed of Kovar or other selected material having relatively low thermal conductivity. The opposite end of the support member 27 is secured throughout its periphery to and supports& disc-like cathode emitter 28 formed of nickel or like material Which carries either thereon or therein a material which is capable, when heated, of emitting copious supplies of electrons. The emitter is connected adjacent its periphery to the support foil 27 and is disposed with its effective electron emitting surface adjacent and parallel-to the grid 16 and in coaxial predetermined spaced relation thereto. i

It is apparent that the terminal 19-20 and support foil 27 form one side of a circuit to the emitter 28. The circuit is completed to the second terminal 26 through a filament or heater coil 29 which is positioned in close proximity to the emitter 28, preferably within a cupshaped portion 30 thereof. The heater coil has one end connected by a metal supporting conductor 31 to a metal disc 32 which is sealed throughout its periphery to the inner wall of the second terminal 26 and thus also forms a portion of the envelope 10. The other end of the heater coil 29 is connected by a supporting conductor 33 to the cathode supporting ring 24 and thereby to" the first cathode terminal 1920. Thus, a circuit is completed through both the emitter 28 and the heater coil 29. Upon application of suitable electrical energy to the cathode terminal, the heater 29 will raise the temperature of the emitter 28 whereupon a copious supply of electrons will be produced, the electrons flowing to the anode 13 under control of the grid 16 in the normal operation of a tube of this type.

The cup-shaped portion 30 of the emitter structure is preferably an integral tubular member depending from the under side of the main disc-shaped portion 28 and closely encircling the heater coil 29 so as to confine as much heat as possible to the central portions of the emitter. In such an arrangement the tubular member 30 will acquire a considerable amount of heat which will be transferred to the electron emitting surface of the emitter.

It has been found to be practically impossible to completely outgas an electron tube, during manufacture thereof, by conventional methods. Therefore, continuous gettering means is required for removing from all the elements within the envelope such gases as may appear during operation of the tube.

attain the highest levels. provide a getter which will operate satisfactorily at or near the relatively high temperatures reached by parts of the cathode structure as well as throughout the range .of operating temperatures of the parts, for example, be tween approximately 300-700 C. Materials such as titanium, zirconium and tantalum are known to function satisfactorily as gettering materials at such relatively high temperatures and can be readily manufactured in the form of thin foils which, when used in the manner taught lherein, extend into the areas of the cathode structure which operate at the highest temperatures, and can be made also to extend into the cooler areas of thestructure as well.

Therefore, the present invention relates to the use of a foil 34 of gettering material which is mounted on the tubular member 30 which encircles the heater coil 29. Since the getter foil 34 may alloy with the material of the member 30 and emitter28,particu1arly in the case of zirconium, titanium or tantalum, the getter .foil is spaced slightly from the member '30: but is connected thereto by suitable means such as an annular ring 35. The connector 35' must be formed of a material which will not alloy with the foil, such as platinum or other selected material. The getter foil 34 ispreferably formed to a tubular shape with one end terminating adjacent, but slightly spaced from, the disclike portion of the emitter 28. The foil may be as long as desired so as to extend to the desired extent into cooler areas of the structure, as shown by dotted lines 36. Thus, such a getter is able to perform its gettering function throughout a wide range of temperatures, such as approximately from 300 C. to 800 C., since some portion of the foil will always be positioned in an area having a temperature at'which the gettering occurs most eflilciently, An additional advantage of .a structure of this type is that the getter foil 34 also provides a heat shield for the inner surface of the cathode-supporting foil'27, which further improves the overall cathode operation.

It will be apparent from the foregoing description that all of the objects and advantages of this invention have been accomplished by the provision of the novel gettering device described hereinbefore. It is also apparent, however, that certain changes may be made without departing from the spirit of the invention.

I claim:

1. A cathode structure for electron tubes, said structure comprising a metal emitter having an integral substautially tubular extension on one side thereof, a heater relatively closely confined within the extension for heating the emitter and extension, a tubular support having one end secured to the periphery of the emitter and extending in encircling relation parallel to and spaced from the extension, a getter encircling the extension and located between it and the support, the getter being a material which readily alloys with the material of the extension, and means mounting the getter on the outer surface of the extension in closely spaced relation there'- -'to comprising a strip of material which is non-alloying with the getter and extension at tube operating temperatures.

2. A'cathode structure for electron tubes, said structure comprising an emitter having an integral substantially tubular extension on one side thereof, the emitter and extension being basically nickel, a heater relatively closely confined within the extension for heating the emitter and extension, a tubular support having one end secured to the periphery of the emitter and extending in encircling relation parallel to and spaced from the extension, a getter encircling the extension and located between it and the support, the getter being' basically of a metal selected from the group consisting of zirconium, titanium and tantalum, and a strip of platinum between the extension and getter and securing the getter in closely spaced relation with the outer surface of the extension.

3. A cathode structure for electron tubes, said structure comprising an emitter having a substantiallytubular extension on one side thereof formed of a selected material, a heater within the extension, a support for the emitter comprising a tubular member encircling the extension in spaced relation therewith and having one end fixed to the emitter, a tubular foil of getter material characterized by its tendency to alloy with the material of the extension, said foil being located substantially coaxially with and between the extension and the support and extending at one end adjacent the emitter and at its other end into a relatively cool area of the cathode structure, and means for supporting the getter foil comprising a strip of material which is nonalloying with the material of the extension at tube operating temperatures, said strip being mounted on the outer surface of the extension and secured to the foil and maintaining the foil spaced from the extension.

References Cited in the file of this patent UNITED STATES PATENTS Germany May 4, I953 

